Dynamic mean field theory of the SK-spin glass

The dynamic infinite range SK model for a spin glass is generalized by considering the bonds as slowly time-dependent. This allows to regularize the long-time behaviour even in the thermodynamic limit, contrary to the corresponding treatment by Sompolinsky and Zippelius. Depending on the order in which limits are taken the model describes annealed or quenched disorder. Below the Almeida-Thouless border of stability the solution found by Sompolinsky and Zippelius is unique unless causality or homogeneity in time are violated.     

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Efficient production of enol ether radical cations by heterolytic cleavage of beta-mesylate radicals

[reaction: see text] alpha-Methoxy-beta-mesyloxy radicals were produced in laser flash photolysis reactions, and yields of enol ether radical cations formed by heterolytic fragmentation of the mesylate group were determined. The mesylate heterolysis reaction is faster than heterolyses of phosphate and bromide groups in analogous radicals and highly efficient in medium-polarity solvents.     

Identification of iron(III) peroxo species in the active site of the superoxide reductase SOR from Desulfoarculus baarsii

The active site of superoxide reductase SOR consists of an Fe2+ center in an unusual [His4 Cys1] square-pyramidal geometry. It specifically reduces superoxide to produce H2O2. Here, we have reacted the SOR from Desulfoarculus baarsii directly with H2O2. We have found that its active site can transiently stabilize an Fe3+-peroxo species that we have spectroscopically characterized by resonance Raman. The mutation of the strictly conserved Glu47 into alanine results in a stabilization of this Fe3+-peroxo species, when compared to the wild-type form. These data support the hypothesis that the reaction of SOR proceeds through such a Fe3+-peroxo intermediate. This also suggests that Glu47 might serve to help H2O2 release during the reaction with superoxide.     

Hydrophobic silica sol-gel films for biphasic electrodes and porotrodes

Hydrophobic sol-gel films from methyltrimethoxysilane (MTMOS) are deposited onto glass and tin-doped indium oxide (ITO) coated glass substrates. Uniform and microporous films of ca. 200 nm thickness are obtained and investigated by scanning electron microscopy and by electrochemical techniques. From cyclic voltammograms for the oxidation of ferrocenedimethanol in aqueous 0.1 M KNO3 apparent diffusion coefficients and free volume data for processes within the film are derived and it is demonstrated that the film morphology can be controlled by the deposition timing. Two novel types of biphasic electrodes for observing liquid/liquid ion transfer reactions are introduced: (i) an ITO electrode coated with a hydrophobic sol-gel film and (ii) a hydrophobic sol-gel film on glass sputter-coated with 20 nm porous gold (porotrode). For the t-butylferrocene redox system deposited in the form of an organic liquid, very low and morphology dependent current responses are observed on modified ITO electrodes. However, the porotrode system allows biphasic electrode reactions to be driven with high efficiency and with no significant morphology effect of the hydrophobic sol-gel film. This type of nanofilm-modified electrode system will be of interest for biphasic sensor developments.     

Isotope selective analysis of CO(2) with tunable diode laser (TDL) spectroscopy in the NIR

The performance of a home-built tunable diode laser (TDL) spectrometer, aimed at multi-line detection of carbon dioxide, has been evaluated and optimized. In the regime of the (30(0)1)(III) <-- (000) band of (12)CO(2) around 1.6 microm, the dominating isotope species (12)CO(2), (13)CO(2), and (12)C(18)O(16)O were detected simultaneously without interference by water vapor. Detection limits in the range of few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. High sensitivity in conjunction with high precision -- typically +/-1 (per thousand) and +/-6 (per thousand) for 3% and 0.7% of CO(2), respectively -- renders this experimental approach a promising analytical concept for isotope-ratio determination of carbon dioxide in soil and breath gas. For a moderate (12)CO(2) line, the pressure dependence of the line profile was characterized in detail, to account for pressure effects on sensitive measurements.     

Formation of compound I by photo-oxidation of compound II

[reaction: see text] Compound I is the heme-iron(IV)-oxo porphyrin radical cation formed in peroxidase and catalase enzymes by reaction with hydrogen peroxide. As an alternative to chemical oxidations of porphyrin-iron(III) species, various compound I species were produced by 355 nm laser flash photolysis photooxidation of the corresponding compound II species, porphyrin-iron(IV)-oxo derivatives. The method is demonstrated by production and kinetic studies of the compound I species from 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron, from horseradish peroxidase, and from wild-type horse skeletal myoglobin.     

Influence of madelung (interatomic Coulomb) energy on Wolfsberg–Helmholz calculations

A model is presented for the estimation of ionicities in molecules and complex ions. The model uses the minimization of total energy by the method of differential ionization energies. The effect of Madelung corrections to the energies is considered, and the model is refined by evaluating the covalent-bond energies. Wolfsberg–Helmholz calculations have been applied to the same type of model, also incorporating Madelung corrections. The Madelung corrections make the metal ionization energy curves less steep, and the ligand ionization energies are nearly invariant with charge. This creates a situation which has previously been artificially imposed by selecting the ligand ionization energies to give desirable terms in the Wolfsberg–Helmholz secular determinant. The effect of Madelung energy is shown to be the primary influence in describing the ionicity and total energy of a chromophore; covalent bonding effects are shown to be secondary when the ligands and the central atom have fairly different electronegativities.     

On the dynamics of phase separation

A new framework is developed for a treatment of the unmixing of an alloy or another system undergoing a phase transition after a quench into the coexistence region. Expanding around a suitably chosen reference equilibrium state new order parameter fields are introduced by a regrouping of diagrams. In a path integral representation the action of the new fields is constructed in a renormalized form and calculated by expansion ind=4– dimensions. As a first application the timedependence of the structure factor is computed using a simple factorization. It is found that unmixing takes place in the whole coexistence régime with a lifetime of metastable states which diverges at the coexistence curve and with no sharp boundary between the spinodale and nucleation régime.